This paper seeks to catalogue the major airborne distance
measuring systems that were developed during the twentieth century. After World
War Two such systems were at the forefront of surveying technology until the
advent of satellite-based surveying and navigation in the 1970s. This catalogue
of airborne distance measuring systems is not exhaustive, with the focus on the
history and use of airborne distance measuring systems used in, or associated
with, the surveying and mapping of Australia.

Electro-optical distance meters were developed from techniques
used to determine the velocity of light. The French physicist Armand Hippolyte Louis Fizeau (1819–1896)
determined the velocity of light in 1849 with his famous cogwheel modulator on
a line of 17.2 kilometres length. This experiment employed for the first time
the principle of distance measurement with modulated light at high frequencies.
Hans Zetsche (1979), stated that the first electro-optical distance meter was
developed by Lebedew, Balakoff
and Wafiadi at the Optical Institute of the USSR in
1936. In 1940, Alfred Huttel published a technique
for determining the velocity of light using a Kerr-cell modulator in the
transmitter and a phototube in the receiver. Huttel’s
work inspired the Swedish physicist, Dr Erik OstenBergstrand to design the first Geodimeter
in 1943 to determine the velocity of light (Bergstrand, 1949 and Bjerhammar, 1972), the name
Geodimeter was derived from Geodetic Distance
Meter (Rueger, 1990).

Electronic Distance Measuring (EDM) is a term that evolved to
describe any electro-optical device or system used to measure distance. Initial
terrestrial and later airborne EDM and the speed of light have thus been
inextricably interdependent. To determine a value for the speed of light the
distance between two points had to be precisely known. Then, with the right
equipment and the known value for the speed of light the distance between any
two points could be determined. As radar based EDM equipment was perfected and
calibrated against lines of already known length, the differences in length,
known versus observed, indicated that the value for the speed of light needed
to be revised. Because of that nexus, this paper contains a section on
refinements of the value for the speed of light stemming from EDM development.

In compiling this paper, a
considerable volume of material was reviewed. The material ranged from
published books to personal accounts; and the facts were not always
consistent or referenced. To provide the most accurate account, original
documentation was sought and this forms the basis of the paper. Where matters
of fact are described they are referenced allowing the provenance to be judged
by the reader should other versions of the facts be read elsewhere.

The names of many of the systems
discussed here are acronyms. Generally, such names should be spelt in capitals.
However, RADAR has developed into common use and today radar is usually
written in lowercase. In this paper, the common presentation of words is used
and most system acronyms have only the first letter capitalised, for example
Shoran. For clarity and consistency, the acronym CSIRO for Commonwealth
Scientific and Industrial Research Organization is used. However, prior to 19
May 1949, this organisation was the Council for Scientific and Industrial
Research (CSIR) and even earlier it was the Commonwealth Institute of Science
and Industry and the Advisory Council of Science and Industry.

Electronic Distance
Measuring

Obtaining distance from electronic instruments is fundamentally
based on the measurement of the time taken for a signal to travel from an
instrument at one station to a distant point and, after reflection or
retransmission there by another instrument set at the point, to travel back to
the trans­mitting instrument. Alternatively, the difference in phase between
the transmission signal and the reflected signal as it leaves and returns to
the instrument at the transmitting station, is measured. When the time taken
and the velocity of travel of the signal are known, the distance between the
two sets of instruments can be calculated. The signal is in the form of
electromagnetic radiation and depending on the purpose the wavelength of the
radiation chosen is generally categorised as being a radio wave, microwave,
including radar, infrared or visible light, including laser. In its infancy,
airborne EDM was known as radar ranging as radar wavelengths were used.

The velocity of travel of
electromagnetic radiation is commonly known as the speed of light. Light is
just a section of the Electromagnetic Spectrum that our eyes can sense and give
us vision. Outside this section within the Electromagnetic Spectrum we have
invisible microwaves and radio waves at one end, and at the other end of the
Spectrum we have the invisible X and Gamma-rays. As light is visible, the speed
of light can be measured and this value was quoted as the velocity of all
electromagnetic radiation. However, as methods were refined, the value for the
speed of light was regarded as the maximum value. But only in a vacuum (in
vacuo) would all electromagnetic radiation travel at that speed. Generally,
EDM signals have to transit the earth’s atmosphere and the friction caused by
travelling through that medium reduced the transit velocity. The closest,
practical calculation of this slower speed is given by formulae which use actual
air temperature and pressure values to model the atmosphere at the time of
measurement for the type of signal emitted. Thus, values for the speed of light
vary depending on whether they are in vacuo, or are from actual free
atmosphere measurement or are from measurements corrected, fully or
partially, for atmospheric effects. To avoid confusion, the values for the
speed of light quoted in this paper contain a reference to their source or can
be considered as the in vacuo value at that time. Further detail on
atmospheric corrections and their application can be found in Rueger (1990).

Initial World War Two Developments

In 1889, Heinrich Rudolf Hertz (1857-1894) a German physicist,
concluded that solid objects interfered with, and scattered radio waves. Thereafter
it was suggested from time to time, that this scattering might be used for
locating obstacles. It was 1932 however, before British Post Office engineers
observed the reflection of radio waves scattered from an aircraft in flight.
Radar (RAdioDetection AndRanging) which can be described as the
science of locating distant objects by radio, was proved by Great Britain
during World War Two.

The breakthrough came with the invention of the magnetron in
1940. Until then the triode tube amplifier was used in many communication
devices and was the basis of the first search radar systems. Because of transit
time limitations, triodes were limited to radio frequencies. Greatly improved
performance could be realised by operating at higher, microwave frequencies,
however no suitable device was then available. The existing klystron,
invented by the Varian brothers Russell and Sigurd in
the United States, was not yet capable of sufficient power for radar applications.

John Turton Randall, Henry Albert Howard
Harry Boot, and James Sayers at Birmingham University in England,
extended the basic idea of the klystron. Their multi-resonator concept
of the magnetron was an extension of the two resonator klystron.
By late February 1940, they had constructed a new type of cavity magnetron,
with a radiation wavelength of 9.8 centimetres. By May 1940, an experimental
radar set using a pulsed, 10 centimetre wavelength, cavity magnetron had
been built at the United Kingdom’s Telecommunications Research Establishment.
The new radar was successfully tested by September 1940. This work resulted in
the Plan Position Indicator (PPI), which even today we recognise as the
most common type of radar display as shown in Figure 1 below.

The basic PPI has the radar antenna at the centre of the display,
thus distances from the antenna are shown as concentric circles. As the radar
antenna rotates, a radial trace on the PPI sweeps the dial in unison with the
antenna and maps any reflections. Equivalent PPIs, called the Jagdschloss and Wassermann with a wavelength
of 2 metres were developed by Germany. Such radar systems that just detect the
radiation reflected from an object are called primary radar. In
contrast, most of the EDM systems that are discussed below are classed as secondary
radar. Secondary radar systems not only comprise a transmitter but, depending
on the system, have one or more responders. These responders receive the
transmitted signal and retransmit it, or respond to it. At the primary
transmitter, the returned signals are received and interrogated to provide the
distance information.

Figure 1 : Generic
diagram of a Plan Position Indicator (PPI) the basis of a search or primary
radar.

The wartime technology push saw the PPI followed by the
British Gee, OBOE, Decca and Gee-H systems, the American Loran, Raydist and Shoran as well as Germany’s and others own
radar developments.

Gee

A blind landing system, using two synchronised transmitters,
was proposed by Robert Bob James Dippy, in October 1937. At the time,
Dippy was working at Robert Watson-Watt's radar laboratory at Royal Air Force, Bawdsey in the United Kingdom. The wartime requirement for
navigation aids rather than landing aids led to a new proposal by Dippy on 24
June 1940. The original landing system design had used two transmitters to
define a single line in space, down the runway centreline. In Dippy’s new concept, charts would be produced illustrating
not only the line of zero difference, where the radar blips were superimposed
like the landing system, but also a line where the pulses were received 1
microsecond apart, and another for 2 microseconds, etc. The result would be a
series of lines arranged at right angles to the line between the two stations.
A single pair of transmitters would allow the navigator to determine which line
they were on, but not their location along it. For this purpose, a second set
of lines from a separate transmitting station would be required. Ideally these
lines would be at right angles to the first, producing a two dimensional grid
that could be printed on navigation charts. To facilitate deployment, Dippy
noted that the station in the centre could be used as one side of both pairs of
transmitters if they were arranged like the letter L, as shown in Figure
2 below. Measuring the time delays of the two outlier slave stations relative
to the centre master, and then looking up those numbers on a chart, an aircraft
navigator could determine his aircraft’s position in space or get a position fix.
The gridded lines on the charts gave the system its name, Gee for the
letter G in Grid.

Figure 2 : Map of
southern Englandshowing a superimposed Gee lattice with Master
station at A and Stations at B and C as the outlier slaves (after Bowen, 1954).

To cover a wider area without having to run cabling hundreds of
miles to connect all the transmitters, Dippy described a new system using
individual transmitters at each of the stations. One of the stations, a master,
would periodically send out its signal based on a timer. The other stations, slaves,
would be equipped with receivers listening for the signal to arrive from the master
station. When the slave stations received the master’s signal,
they would respond by sending out their own broadcast. This would keep all the
stations synchronised wirelessly. Dippy suggested building installations with a
central master and having its three slaves about 80 miles (130
kilometres) away and arranged roughly 120 degrees apart, forming a large layout
in the shape of the letter Y. A collection of such installations was
known as a chain, an example of which is shown in Figure 3 below.

Experimental installations were already being set up in June 1940,
and by July 1940 the system was usable to at least 300 miles (450 kilometres)
at altitudes to 10,000 feet. On 18 August 1941, British Bomber Command ordered
the Gee aircraft sets into production at Dynatron Radio Limited and Cossor Radar Limited, with the first mass produced sets
expected to arrive in May 1942. In the meantime, a separate order for 300
handmade sets was placed for delivery on 1 January 1942 which was later pushed
back to February 1942. Overall, 60,000 Gee sets were manufactured during World
War Two. These sets were used by the Royal Air Force, the United States Air
Force and the Royal Navy. A Gee Mark II was also developed to overcome jamming.
By the time it became operational in February 1943, it had been selected for
use by the United States 8th Air Force.

By 1948, seven Gee chains existed: four in the United Kingdom, two
in France and one in Germany. Gee developed into one of the most widely fitted
airborne radio navigation aids of the day. Mobile transmitting stations for Gee
were also developed. The first of these went into operation on 1 May 1944 at
Foggia in Italy, and was used operationally for the first time on 24 May 1944.
Other units were sent into France soon after D-Day. Preparations started for
Gee transmitters in Nablus, Palestine, to guide flights across the Middle East
but world events removed this requirement. Gee was finally shut down by 1970
but the principles behind Gee became the basis for what are generically called Hyperbolic
Systems.

Bob Dippy's expertise saw him later recruited to the staff of the Woomera Rocket Range in Australia. During the instrumentation period Dippy joined the Long Range Weapons Establishment (LRWE) in late 1957 as Principal Officer in the Radio Frequency Techniques Group. Dippy was soon given overall authority for timing and his first task was to establish a dedicated timing section in his group, renamed Electronic Techniques (ETQ).

Hyperbolic Systems

These navigational systems required three ground stations with the
necessary equipment as well as equipment in the mobile element be it vessel or
aircraft. The measured quantity was the difference in distance between two
fixed stations and the mobile element. This difference did not fix the
position of the mobile element but defined a hyperbola, with the ground
stations as foci, on which the position of the mobile element must lie.
Consequently, the third ground station was required, and the observations of
the difference in distance from it and from one of the other two stations to
the mobile element then defined another hyperbola on which the mobile element
must also be situated. Hence, the position of the mobile element was given by
the point of intersection of the two hyperbolae. As with the Gee system, the
hyperbolic systems’ ground stations were not independent of one another, and
the use of master and slave ground stations meant that they were interlocked
so that the choice of ground sites for this system was limited. This limitation
was overcome, however, by establishing a chain of ground stations.

The Americans were not far behind the British Gee implementation with
the development of their own system. Loran (Long Range Navigation),
now identified as Loran-A, was developed by the Radiation Laboratory of the
United States’ Massachusetts Institute of Technology during 1941. This
development work was supervised by the National Defense
Research Council. Around mid-1942, Bob Dippy went to the United States
for eight months to assist in Loran development. Many of the techniques Dippy
used in Gee were adopted, and it was Dippy who insisted that the Loran and Gee
receivers be made physically interchangeable so that any Royal Air Force or
United States of America Air Force aircraft fitted for one could use the other
by simply swapping units. This was to prove invaluable long after the war had
ended, as Transport Command navigators flying the Australia run from the
UK could plug in the appropriate set depending on where they were.

The first demonstration of Loran-A was on 12 June 1942, with
equipment installed on the airship K-2. This was followed on 4 July 1943, by
the first readings from a Boeing B-24 aircraft. The first observations from a
ship were made on a Coast Guard Cutter from 18 June to 17 July 1942. The
observations during that period indicated a total range of 1,400 nautical miles
was achievable with Loran-A. These results were considered good enough to
warrant the expansion of the system and its recommendation to navigational
agencies. On 1 January 1943, the administration of Loran-A was officially
transferred to the United States Navy.

The range and relatively high order of accuracy of the Loran-A
system came from its use of the more stable and reliable propagation
characteristics of radio waves. The Loran-A system could be used for distances
up to about 1,400 nautical miles at night and 700 nautical miles by day, with
an accuracy of better than 0.25 nautical miles or 450 metres. Although useful
for ordinary navigational purposes, Loran-A was not accurate enough in itself
for survey work. Consequently, the United Sates Coast and Geodetic Survey, Radiosonic Laboratory, later evolved an Electronic
Position Finder (EPF). The EPF combined the main features of the shorter
range Shoran with those of the longer range Loran system, so that it was now
possible to fix the position of a survey ship accurately enough for hydrographic
charting purposes. This system was initially called the Radio Ranger and
after two years of testing and modification, it was used operationally in the
Gulf of Mexico in 1947. The system was capable of 50 to 75 metre accuracy at
ranges out to 300 kilometres.

In 1938 in Germany, Dr Ernst Kramar
(said to have been working at Standard Elektrik
Lorenz) developed an improved version of the Radio Ranger. However, as
Standard Elektrik Lorenz (SEL) did not exist until
1958, Kramar was more likely to have been employed by
its predecessor C Lorenz AG (AG was short for Aktiengesellschaft,
the German equivalent of Corporation). Kramar's
initial hyperbolic system was called Elektra and a later improved
version was called Sonne (Sun).
Operating at other frequencies, there was also to have been Mond
(Moon) and Stern (Star). Sonne was
installed in Norway, France and Spain as a navigational aid both for German
aircraft flying the circuitous route over the Atlantic between France and
Norway, and for the German U-boats. Following their acquisition of Sonne charts and a receiver, the British made use of
Sonne under the name of Consol
meaning by the sun. (See Proc (2015) for a
summary of other hyperbolic radionavigation systems.)

Germany didn’t persist with hyperbolic radionavigation systems
after World War Two. In contrast, the United States Loran-A network consisted
of over 70 transmitters and provided coverage over about one third of the
earth’s surface. In the late 1940s and early 1950s, experiments in low frequency
Loran produced a longer range, more accurate system. Technical problems
resulted in Loran-B never becoming a commercial system and was eventually
surpassed by Loran-C. Loran-C provided longer range and greater accuracy when
it first came into operation in 1957. Using the 90-110 kHz band, Loran-C
operated in parallel with Loran-A until the mid-1970s, providing navigation
assistance throughout the area shown in Figure 4 below. The United States
continued operating Loran-C until the network’s closure in the mid-1990s.

Figure 4 : Map
illustrating the global coverage of Loran.

(from Proc (2015)
originally attributed to Eurofix web page).

F0rom 1936 to 1939, William Bill Joseph O'Brien had been
working independently on a method of measuring the ground speed of aircraft.
His system was called the Aircraft Position Indicator (API). At the
outbreak of World War Two the American government and civilian authorities were
uninterested in O'Brien’s API. O'Brien then offered his idea to the British Air
Ministry through his friend Harvey Fisher Schwarz. Schwarz was an American then
working in London for the Decca Record Company Limited. This company was
previously known as the Decca Gramophone Company Limited and had a sister
company Decca Radio and Television Limited, both of which were London based.
The later success of O’Brien’s work spawned the Decca Navigator Company. With
this proliferation of the Decca name, and with some equipment bearing only the
brand name Decca, it is often difficult to trace the exact source of
some Decca equipment.

With D-Day looming, the British Admiralty wanted to guard against
the jamming of their Gee system and so took an interest in O'Brien’s API
in 1941. Trials were organized off Anglesey in mid-1942 using a master
unit transmitting at 300 kHz and a slave unit transmitting at 600 kHz.
Successful comparison of the signals was made at 1200 kHz and further research
by Decca Radio and Television Limited was then undertaken with assistance from
the Admiralty Signals Establishment. Early in March 1943, Decca was given the
order to produce 27 receivers plus the driver and phase control units needed
for the transmitters. All equipment was delivered by mid-May 1943 when the
Royal Navy began its D-Day training and preparations in earnest. In January
1944 a test of Decca on new frequencies was carried out in the Irish Sea and it
was also compared with the Royal Air Force Gee system for accuracy. Although
Gee and Decca were similar in broad principles, Decca was considered more
accurate than Gee and in today’s terms more user-friendly, because the
results were presented directly on clock dials called decometers
instead of a cathode ray tube as in Gee. Figure 5 below is a photograph of
Decca’s decometers. One disadvantage of the early
Decca sets was the need for the decometers to
be initially set up using an accurately known position. If there was a break in
reception for any reason, the decometers
had to be recalibrated.

Figure 5 : Decca’s decometers.

Post war, the Decca system was largely applied to hydrographical
surveying. Ranges up to 400 miles (650 kilometres) were obtained over water. The
accuracy varied with the position of the point to be fixed relative to the
three shore stations. Experience showed it to be suitable for both inshore and
offshore hydrographical work. Decca was also used satisfactorily for tracking
strips of aerial photography for British Ordnance Survey’s large scale mapping.
Decca’s range and accuracy came from it operating on wavelengths of several
kilometres. These low frequency wavelengths tend to follow the earth’s
curvature for very long distances at a speed of propagation mainly related to
the medium over which they travelled. Decca was adapted for best accuracy over
sea water. However, over land with its constantly changing density and nature
of the earth's surface, the same accuracy could not be replicated.

Raydist, from a
mix of the words Radio and Distance was a post war system, first
mentioned as being in development on 18 April, 1947. The system was developed
by the Hastings Instrument Company of Hampton, Virginia USA, which was founded
in 1944. The hyperbolic type N (for Navigational) Raydist
permitted multiple users in the same net and gave an accuracy of about 15 to 30
metres at a distance offshore of 80 kilometres. A type DM (for Distance
Measuring) Raydist was produced as well as other
variants. The DM Raydist operated at 3 MHz and was
accurate to under 1 metre at over 400 kilometres. In the days before GPS, DM Raydist was used to calibrate the Inertial Navigation
Systems on early nuclear submarines.

OBOE

While Gee had successfully impacted wartime aircraft navigation,
cloud below 20,000 feet obscuring the target meant a stand down which
frustrated the commanders and air-crew of Bomber Command. British wartime Prime
Minister Churchill thus gave high priority to developing improved methods of
navigation and accurate payload delivery despite cloud or haze. OBOE was
proposed by Alec Harley Reeves and his co-worker Frank Jones at Britain’s
Telecommunications Research Establishment. Operational in late 1942, the OBOE
system required two transmitters initially based at Dover and Cromer. The two
ground stations both emitted streams of pulses on the same carrier frequency,
but at differing intervals. The aircraft carried a responder, which replied to
the interrogations of both ground stations so that each ground station knew the
range to the aircraft. Operationally, the aircraft flew a course of constant
radius about the tracking station Dover, the course radius being such as to
bring the aircraft over the target. When the aircraft arrived at a precise
distance from the releasing station Cromer, a signal was sent automatically
which released the payload. Please refer to Figure 6 below. The pulses from the
tracking station were commonly sent at a frequency of 133 pulses/second and
modulated by Morse signals to convey information to the aircraft’s crew. Thus
if the aircraft was at too short a range a series of dots was sent. If at too
great a range, a series of dashes was sent. When the aircraft was on track a
constant tone like that from the orchestral instrument the Oboe was heard.
Hence the name OBOE. The technology, however, limited the use of OBOE to
one aircraft at a time. Germany improvised a system conceptually similar to
OBOE, code named Egon.

Figure 6 : OBOE’s
operating principle (after Bowen, 1954).

It is interesting to note that even in these early days of
airborne EDM that the historical, insular, territorial map datums
caused problems. Such were the differences between these datums
that they could be detected indirectly by these early airborne systems (Bowen,
1987). Based on existing map data, point to point distances across historical
map boundaries would be determined. The radar would then direct an aircraft
based on those distances. European map datums caused
the determined distances to be incorrect and as a consequence the required
location was not being overflown. Once a datum difference had been identified
and quantified, appropriate operational adjustments could be made. Although
unknown at the time, this was probably the first attempt at comparing
intercontinental map datums. Please refer Annexure C below.

Gee-H

The name Gee-H is confusing, since operationally the system
was similar to OBOE and not very much like Gee. The name was adopted because
the system was based on Gee technology. It operated on the same range of 15 to
3.5 metre wavelengths or frequencies of 20 to 85 MHz, and initially used
the Gee display and calibrator. The H suffix came from the system using
the twin-range or H-principle of measuring the range from
responders at two ground stations. While Gee-H was about as accurate as OBOE
with a range of about 300 miles it could be used by as many as 90 aircraft at
once. For this number of aircraft to uniquely recognise the responses to their own
transmissions, the pulse recurrence frequency was jittered
automatically, that is the inter-pulse timing was altered. Only the signals
with the same inter-pulse timing would be recognised by the device in a
particular aircraft. The time taken by a ground station to receive a pulse,
send out the response and return to the receiving condition, was about 100
microseconds. With a pulse recurrence frequency of 100 cycles/second a ground
station would be busy for 10,000 microseconds in any one second dealing with
the enquiries of one aircraft. A Gee-H ground station would therefore have
990,000 microseconds free in each second in which to respond to other aircraft,
giving a theoretical maximum handling capacity of 100 aircraft. When Gee-H
became operational in 1944, maximum handling capacity of the stations was not
achieved hence the more practical limit of around 90 aircraft per station was
adopted.

The Gee-H system required two ground stations already fixed by
ground survey methods and about 100 to 120 miles (200 kilometres) apart. The
air­craft carried a pulse transmitter and receiver and pulses were sent to each
ground station responder in turn. The responders returned the pulses to the
aircraft on a different fre­quency. Here the return pulses were received and
the time interval between transmission and reception was recorded or measured.
The transmission of pulses, that is intense bursts of energy which
lasted a very short time and were then repeated after a relatively long period,
gave the radiated energy time to travel to the distant responder and then
return to the transmitter’s receiver before the next burst was emitted. In this
way, no confusion or interference in reception was likely to arise between the
outward and returning signals. With a suitable electronic display and a large
number of repetitions of the bursts, the emitted and received signals could be
made to form images which could be seen by eye or could be photographed as a
continuous picture. The derived measurements gave the distance from the
aircraft to each ground station responder. With the height of the ground
stations known from the ground survey data, and that of the aircraft obtained
from altimeter readings, the aircraft to ground distances could be easily
reduced to the equivalent arc lengths at sea level. Accordingly, the lengths of
the sides of a spherical triangle became known and the triangle could, if
necessary, have been solved to give the three respective internal angles.

Transmitters on the ground as used by OBOE, meant that the ground
equipment could be larger, more complex and powerful. Smaller, lighter
transponders went into the aircraft. The signal information was thus
distributed between two ground stations, while other important information like
altimeter readings, was collected in the aircraft. Recording therefore had to
be done at three points and the times correlated. It was found more preferable
to retain the transmitter in the aircraft and focus all the data gathering
there as with Gee-H.

The wartime need to make maximum use of existing Gee equipment in
Gee-H, while practical, forced the use of less accurate, lower frequencies. To
obtain greater accuracy a higher frequency should have been chosen. When
designed, the American Shoran system was able to employ a higher frequency and
replace Gee-H.

British Colonial Mapping with Gee-H

As in wartime, the ability of Gee-H and the later Shoran system to
fix the position of an aircraft was found to be just as advantageous in
peacetime. The mapping of dangerous or hard to reach places, or where
traditional survey and mapping was just not possible, could now be achieved
using airborne methods. By judiciously establishing a relatively few fixed
points on the ground to site responder beacons, vast regions could be accurately
photographed from the air almost without needing to set a foot on the ground.

Initial development work was carried out by the War Office from
1943-45 when British Brigadier Martin Hotine was
Director of Military Survey. Investigations were carried out in cooperation
with the British Air Ministry, the Ministry of Aircraft Production, and the
Telecommunications Research Establishment. These investigations were supported
by Survey Units of the Royal Engineers, Royal Canadian Engineers and the United
States Corps of Engineers and others. British Major Cecil Augustus Hart was
responsible for the research work related to surveying.

With the transmitter and measuring equipment in the aircraft the
capability of Gee-H made it ideal for use in the British Colonies. Under the
Directorate of Colonial Surveys, photogrammetric mapping on the scales of 1:50,000 and 1:25,000 was successfully undertaken in Ghana,
Gambia, Sierra Leone, Rhodesia, Nigeria, Gold Coast and Tanganyika. Topographic
maps were needed for various colonial development schemes. These schemes
included a railway link between East and Central Africa, irrigation projects in
Basutoland, hydroelectric undertakings in Rhodesia and West Africa,
international boundary definition, and agricultural and mineral developments in
other parts of the African continent.

From 1946 to 1952, No.82 Squadron of the Royal Air Force had its
base near Nairobi in Kenya. The Squadron was equipped with seven Avro Lancaster
MK.1 aircraft for photography operations. Its two Douglas Dakotas handled
passenger and freight carrying tasks. The Dakotas were also used for
supply-drops to the parties manning the remote Gee responder beacon sites. The
Squadron initially used the American K17 aerial survey camera but in August
1951 changed to the F49 being the RAF designation for the Williamson Eagle IX
aerial survey camera. The improvement in photographic quality was most
noticeable due to the Williamson camera’s improved optics and the
pressure-plate system for holding the film in perfect register with the focal
plane. With a six inch focal length lens, a nominal photoscale
of 1:30,000 could be achieved except in extreme cases
as the Lancaster’s were incapable of reaching altitudes above 23,000 feet.

It had been initially hoped that, by using two radar stations, it
would be possible to fix the positions of the photographs with sufficient
accuracy to allow the maps to be plotted without surveyors going in on the
ground. Although this was done later in Gambia, it was generally found to be
impractical (Macdonald, 1996).

Four mobile Gee-H responder units gave the aerial photographic
program flexibility of operation. The Gee-H responder sites were situated on
suitable high points whose position was fixed by prior astronomical observation.
Operationally, the aircraft was guided by the navigator with his Gee-H unit
towards an established ground responder. At the predetermined distance from the
responder the aircraft would be turned onto a course for the photography
acquisition. This course would be the arc of a circle so the aircraft was
continuously turning. The Gee-H unit would indicate any deviation from the set
course. A near vertical photograph was required about every 20 seconds.
Accordingly, just before an exposure a red light showed in the cockpit to warn
the pilot to fly the aircraft exactly level for that instant, before returning
to course. For the aircrew it was a difficult and exhausting task. Owing to
this mode of operation over circular tracks, it was impossible to work closer than
30 miles to the Gee-H responder. Conversely, owing to erratic reception,
operations were unsatisfactory at distances much greater than 200 miles from
the Gee-H responder. Accurately plotted ground control points in addition to
the Gee-H responder beacons were used to relate the acquired photography to the
ground to confirm coverage or indicate gaps. Please refer to Figure 7 below.
Even the most expert aircrews failed to get perfect coverage and filling in the
gaps was the most difficult job of all. More detail including specifications
and operational requirements can be found in Hellings’
1954 paper Radar Controlled Air Survey Photographic Operations in Africa
1946–1952.

Figure 7 : Courtesy
Flight Magazine, 14 November 1952.

The total area covered during the whole six years of operation was
1,216,000 square miles. This involved an average of 8,000 negatives taken and
processed each month and the operating of Gee-H responder beacons at 44
separate locations. In addition to the large aerial photographic program in
Africa, a Mosquito Squadron, based on Singapore, flew similar photographic
operations in Malaya, North Borneo and Sarawak.

Shoran

Across
the Atlantic, the Americans had continued with their own wartime airborne EDM
development efforts. In 1938, Stuart William Seeley an engineer with the Radio
Corporation of America (RCA), found he could measure distances by time
differences in radio reception. In mid-1940, Seeley proposed building Shoran
for the US Army Air Force and by late 1944 Shoran was in operation in Italy.

The
official long name for Shoran is SHort-RAngeNavigation, (Rabchevsky, 1984). However,
former US navigators and bombardiers used the long form name SHort-RAngeAid to Navigation.

During
the system's development, Seeley and an RCA manager flew to England to describe
the system to American and British Air Force personnel. There they observed the
OBOE system which could only guide a single aircraft, whereas multiple aircraft
could be guided by Shoran. The Shoran system, used carrier frequencies of 230
to 250 MHz (wavelengths of around 1 metre). By contrast, the British Gee and
Gee-H systems worked on frequencies of about 30 to 43 MHz (wavelengths of 10 to
7 metres). With Shoran, the transmitting frequencies were switched in turn so
that the ground station responders were alternately interrogated at intervals
of a twentieth of a second, and both ground stations responded on a frequency
of 300 MHz. The intervals were regulated by crystals
in the responders which were thermostatically controlled, and by a crystal in
the aircraft which was calibrated against the responders while in operation. A
positional accuracy of 20 yards in 200 miles (7 metres in 100 kilometres) or
better than 1:15,000 could be achieved. Kroemmelbein’s 1948 paper Shoran for Surveying, provides
details of the Shoran electronics.

About the
time Shoran became operational in 1944, a conference on the future uses of
Shoran was held at Wright Field in Dayton, USA. Two of the attendees were
Lieutenant Commander Clarence Burmister, US Coast and
Geodetic Survey (C&GS), and Lieutenant Colonel Carl Aslakson,
US Army Air Force. Aslakson was a C&GS officer
who was transferred to the 311th Photo Wing for the duration of the Second
World War. During 1944-1945, Burmister was active in
converting Shoran to a hydrographic surveying system, while Aslakson
pioneered the use of electronic systems for geodetic distance measurement
beginning with Shoran.

Up to
1944, measuring ground to air distances was limited by equipment range and
aircraft flying height. In 1945, Aslakson formulated
the use of an aircraft to cross an imaginary line between two Shoran
responders, hence the name line crossing technique. This technique had
the advantage that much longer lines could be measured but the cost was the
need for retransmitting equipment at each end of the line. The technique
required an aircraft to fly across an imaginary line between two ground station
responders, usually at a slight angle to it and near the centre. A series of
simultaneous observations were taken at close intervals of time to each ground
responder. With distances to the aircraft measured for a number of positions on
each side of the direct line between the two ground stations, the sum of the
distances was obtained. The results were plotted as a curve against time and
the minimum sum for all possible positions of the aircraft on the line of
flight obtained. More frequently however, the minimum sum was obtained
analytically from a least squares solution. The minimum distance obtained after
reduction to the arc length at sea level was the required length of the direct
line. This method of measuring the lengths of long lines was known as radar
ranging.

During
all line crossing measurements, the aircraft was kept at a constant altitude as
measured by an altimeter. The elevations of the end stations had to be known or
determined by ground parties. Observations for pressure and temperature were
taken at timed intervals at the ground stations and were also recorded in the
aircraft.

The same
method could be used for calibrating the airborne EDM equipment. Here the
flights were made across a line whose length had already been determined by
ground survey methods. The difference between the line length obtained by radar
ranging and that determined by ground methods gave a correction which could
be applied to other measurements made with the same equipment.

Using
what Aslakson and Rice reported in their 1946 paper, Use
of Shoran in Geodetic Control, as refined Shoran operating methods,
six lines of a first order geodetic triangulation network were measured using
the line crossing technique. With the elimination of any systematic error and
by observing the line crossing for any given line more than five times at
least, the precision of the determination of the length of a single line could
be increased and an accuracy of something like 1:20,000
(5 metres in 100 kilometres) obtained.

Between
1947 and 1949 Canada undertook the development of Shoran for surveying and
mapping. The Royal Canadian Air Force (RCAF), National Research Council (NRC),
Dominion Meteorological Service and the Department of Mines and Technical
Surveys all participated in this development. Testing was conducted in the
Ottawa area over several long lines of the Canadian first order triangulation
network. The RCAF’s 408 Squadron was later tasked with the Shoran survey of
Canada. The 408 (Goose) Squadron was a famous wartime unit. It was re-formed at
Rockcliffe on 10 January 1949. The Squadron operated
eight Lancaster MK.X modified aircraft, four of which were equipped with Shoran
sets. The Shoran survey started with the measuring of the line between the
points, Sprague and Camp Hughes, just South of Winnipeg, which
were already tied into the United States’ own survey. These connections enabled
the Shoran survey to use the North American Datum 1927 (NAD 27) with its origin
at station Meades Ranch. Shoran then
formed a trilateration connection with the survey at Edmonton. The resulting
small survey misclose further validated Shoran’s
capability. (Trilateration is a survey method where the lengths of the sides of
triangles are measured. It is a different approach to the classical survey
triangulation method where the angles within the triangles were measured.)

The
Canadian Shoran survey took until 1957 to complete and provided the control
required for 1:250,000 scale topographic mapping in the remotest areas of
Canada. Some 143 points were connected by 502 lines. The longest line was 367
miles. An overall accuracy of 1:56,000 was achieved. Between the Shoran fixed points
other minor control points were fixed from aerial photography by aerotriangulation, the latter points being adjusted to the
points established by Shoran. Such was the success of this survey that when
Shoran is mentioned the Canadian survey immediately comes to mind. A map
showing the extent of the Canadian Shoran survey is at Annexure
A, Map A1.

The
Shoran airborne equipment as shown in Figure 8, weighed about 340 kilograms. With
the addition of two operators the aircraft used had to carry a payload of some
600 kilograms. At each ground station there was a responder beacon, which with
its power supply weighed 680 kilograms. Each ground station also required two
operators plus a 250 litre drum of petrol to fuel the power generator.

Figure 8 : 1949 photograph
of operator with CSIRO with a Radio Corporation of America (RCA) Shoran
aircraft set AN/APN-3 in Douglas Dakota C47B aircraft.

The following procedure was generally followed to achieve a Shoran
line crossing. The aircraft navigator, who was provided with special equipment
to enable him to know his approximate position at any moment, warned the Shoran
operator when some distance away from the point where he expected the aircraft
to cross the line. The Shoran operator then searched his oscilloscope to pick
up the signals from the port and starboard responders at the ends of the line.
These were called the drift and rate ends respectively. After
picking up these signals, which were indicated by pips on a circular trace on a
cathode ray tube, he followed them as the aircraft approached the mid-point of
the line. By turning two handles, the operator could bring the ground signals
into coincidence with a marker pip and then kept all three in
coincidence until the navigator informed him that the line crossing was
complete. Meanwhile, shortly before he considered the aircraft was about to
cross the line, the navigator switched on the recording camera. This camera
photographed the dial panel of the Shoran set at prearranged intervals of three
seconds, and after 60 frames were acquired, he switched the camera off again.
This completed one line crossing. The photo­graphs
taken on 35 mm film, were subsequently enlarged to extract the recorded data.
The frames showed the two dials where the distances to a thousandth part of a
mile, or about 1 metre, to the drift and rate stations at the
moment of exposure were indicated. Other dials included in the 35 mm photoframes recorded orientation, temperature, time and
altimeter, the frame number and the run number. After four line crossings a
second Shoran operator took over the duties of the first, and another four line
crossings were made. On a separate day, and in theoretically different
meteorological conditions, another sequence of two sets of four line crossings
were made. Each line was therefore measured at least sixteen times in different
atmospheric conditions.

The Canadian work showed that the ground station responder
crystals needed to be calibrated before and after each working season, but were
generally found to have kept their frequency to within 2 parts per million. A
constant delay also occurred at each responder which was determined before and
after each operating season. Even so, the resolution of Shoran meant that a
single measurement could only be accurate to about 8 metres. Larger errors
occurred with the variation of signal strength.

Around the end of World War Two, the then United States Army Air
Force became interested in testing Shoran to determine whether it could be used
for establishing survey control to geodetic standards. From this work emerged Hiran. Aslakson collaborated with
Seeley of RCA, to design a modified Shoran system that would prove to have
accuracies of better than 1:100,000 (1 metre in 100
kilometres). For proof of concept, Aslakson set
responders on known first order geodetic points and compared the Shoran derived
distance to the known geodetic distance. He discovered a systematic difference
that ultimately could only be explained by revising what was then the accepted
value for the velocity of light (Seeley, 1961). This aspect is discussed in
detail in the next section.

Figure 9 : 1946
Radio Corporation of America (RCA) advertisement for using Shoran for
surveying.

Industry also saw Shoran as a valuable tool in the post war search
for, and exploitation of, natural resources. Please refer to Figure 9 above.
Surplus Shoran systems became widely used for navigation in the oil and gas
exploration industry. Shoran equipment was deployed to navigate seismic survey
vessels and position drilling rigs around the world. Truck-portable Shoran
transponders with an antenna up to 90 feet tall (27 metres) were set up
within a few feet of geodetic survey stations near the coast. Shoran chains
consisting of three or four shore stations were used to provide highly accurate
navigation across large exploration tracts that were up to 200 miles
(320 kilometres) offshore. Frequently, the old massive vacuum tube
transmitters were fitted with solid-state control boxes for more reliable
operation and to improve reception of weaker signals over the horizon.

Value for the speed of light

As mentioned earlier, a value for the speed of light was required
to convert the time of travel for a Gee-H, Shoran or later Hiran/Shiran electronic signal to a distance. Table 1 below lists
the values for the speed of light relevant to this paper. The list also shows
the source of the listed value as the value can vary between references.

Person
& method

Year(s)

Speed
of light in vacuo

(kilometres/second)

Albert A Michelson – optical

1926

299,796 ± 4
(1)

CA Hart (1948) after AA Michelson

1929-33

299,774 ±
11 (1)

Wilmer Anderson - optical

1939-41

299,776 ±
4 (1)

JJ Warner (1947) after RT Birge (*)

1941

299,776 ±
4 (1)

FE Jones & EC Cornford – OBOE

1949

299,783 ± 25
(2)

Erik Bergstrand - Geodimeter

1949

299,796 ±
2 (4)

Carl Aslakson –
Shoran

1949

299,792.4 ± 2.4
(3)

Louis Essen - cavity
resonator

1950

299,792.5 ±
1 (2)

Carl Aslakson – Hiran

1951

299,794.2 ± 1.4
(3)

Keith Froome - radio
interferometer

1951

299,792.6 ± 0.7
(4)

Trevor Wadley –
Tellurometer

1956

299,792.9 ± 2
(4)

Accepted

Today

299,792.458
(4)

The values are taken from original papers (1) Warner 1947, (2)
Essen 1952, (3) Aslakson 1951, and (4) http://www.ldolphin.org/cdata.txt.
Also referBjerhammar (1972).

Table 1 :
Measurements of the speed of light relating to airborne EDM.

As mentioned above, Cecil Augustus Hart had been responsible for
the research work in developing airborne EDM for surveying. In his 1948 paper,
Hart stated that the fundamental velocity of the propagation of light in
vacuo had been derived by optical methods over many years. Hart added that
a recent value accepted for radar navigation throughout the War was 299,774 ±
11 kilometres/second. Michelson and others (1935) derived this value from
2885.5 determinations of the velocity, during the period September 1929 to
March 1933. These determinations were achieved despite Michelson’s death on 9
May 1931 when only 36 of the 54 series of observations taken during 1931, had
been completed. Earlier, a 1924-26 series of measurements of the velocity of
light had given a value of 299,796 kilometres/second which was interesting in
the light of future events; please refer to Table 1 above.

During 1946, the British had carried out experiments using OBOE
from a station in North Devon and a Mosquito aircraft. Firstly, the Mosquito
was flown across an extended base line between two geodetic stations as nearly
as possible on a predetermined tracking range. Then the aircraft flew tracks of
three different radii from the OBOE station. There had also been earlier
experiments using Gee-H during the war over two ranges in the South of England.
Gee-H equipment, although less accurate than OBOE had to be used for
operational reasons. The main purpose for these tests was to gain data on how
flying height and distance from the responder beacon affected the speed of
light.

When the values for the speed of light that resulted from all of
this work were used to compute distance they gave measures of accuracy for
OBOE and Gee-H within the range of 5 to 13 metres. Francis Edgar Jones and
EC Cornford (Hart, 1948), are credited with
concluding that their airborne EDM distances only matched already surveyed
distances if the value for the velocity of light was increased by nearly 14
kilometres/second. That is from Michelson’s accepted value of 299,774
kilometres/second up to 299,788 kilometres/second.

Following the development of Shoran in mid-1945, a
British-American team used Shoran to measure a 618.369 kilometre line in Italy.
The American Shoran system used Wilmer Anderson’s 1939-41 value of 299,776
kilometres/second for
the speed of light in preference to the earlier
British value of 299,774 kilometres/second used in OBOE and Gee-H. In this
experiment the aircraft was flown 22 times across the line between the ground
station responders. During each crossing the minimum distance was observed, and
later reduced to a sea-level distance. The line crossings were made at
altitudes of 11,000 and 15,000 feet. The mean of the Shoran derived distances
was 618.320 ± 3.5 metres an accuracy of only 1:13,000.
If Essen's later value of 299,793 kilometres/second for the speed of light were
used instead of the 299,776 for which the Shoran computer was designed, the
discrepancy would have been reduced to 5 meters, an accuracy of better than 1:120,000.

In mid-1949, Aslakson reported on his
most recent Shoran work. A network of 47 lines varying in length from 67 miles
to 367 miles (105 kilometres to 590 kilometres) were measured using the line
crossing method. Six of the lines measured could be directly compared with
geodetic distances previously obtained from first order triangulation. The
entire network however, was so designed that a rigid adjustment was also able
to be made. From the comparison with the six geodetic lengths and from an
adjustment of the 41 other lines, a value for the speed of light of 299,792.4
kilometres/second was derived. Using this new value for the speed of light the
accuracy on 41 of the 47 lines exceeded 1:25,000 (4 metres in 100 kilometres).

To achieve the above results, refined Shoran measuring and
distance derivation procedures had been adopted. Specifically: flying the line
crossings so as to eliminate observer's errors, using a least-squares
computation to calculate the minimum sum distance, improving the measuring of
the aircraft’s altitude, applying an atmospheric correction based on actual airborne
weather reconnaissance at the time of the line crossing, and modifying the
geometric corrections for the reduction of the slant Shoran distances to
sea-level distances or to the approximate geodesic. These procedures were in
addition to extensive instrument research that resulted in numerous
modifications of the Shoran system. The most important of these was the
discovery of an error which was due to changes in the intensity of the signal
and the design of a method to correct for this error. Many of the instrumental
changes were suggested by RCA’s Shoran inventor Stuart Seeley. While some
attempt was made to maintain signal intensity during this project it was not
done consistently.

Nevertheless, the above improvements led to the development of what
was to be later called Hiran. Hiran
is discussed in detail in the next section. The firstHiran system was tested during February and March 1950,
over a network of 15 lines in Florida. The accuracy of the Hiran
measured lines was better than 1:100,000 or 1 metre in 100 kilometres. From
this work Aslakson also derived a new value for the
speed of light being 299,794.2 ± 1.4 kilometres/second.

John James Warner of the Division of Radiophysics
of CSIRO, authored a 1947 paper, The Velocity of Electromagnetic Waves.
Warner examined the work of Raymond Thayer Birge in
correcting various values previously found for the speed of light and
establishing them on a common basis. Warner concluded that Birge’s
value (refer Table 1 above) was probably the best at that time. Soon
thereafter, Warner was to lead Australian tests of Shoran which are fully
described below. Hart (1948) reported the results of early work over a single
line, stating in Australia, experimental work has been carried out on a
ground surveyed distance of first order accuracy of 158.812 ± 0.001 miles (some
256 kilometres). The mean of 46 radar line crossing measurements, when reduced
geodetically, gave 158.848 ± 0.009 miles. At the time of writing the volume of
experimental work is not sufficient to explain the discrepancy of 0.036 miles
(nearly 58 metres or 23 metres per 100 kilometres). As will be seen later
in this paper, by the end of the eighteen months of Australian Shoran testing
the discrepancy had been reduced to around 7 metres per 100 kilometres.

As a result of all this work to determine an operational
value for the speed of light to use with EDM, the then current value was still some16 kilometres/second too slow! Aslakson (1951)
adopted the value of 299,793 kilometres per second for future use with Shoran/Hiran. The report on the 1962-64 Southwest Pacific Survey,
using Hiran, specifically recorded that a value of
299,792.5 kilometres/second was used for the speed of light. This same value was adopted for the speeed of light by the National Mapping Council in their resolution 194.

Technology

Year

Quoted/Derived Accuracy(*)

Location

±m

Ratio

Shoran

Wartime

[20]

1:15,000

Given as 20 yards in 200 miles

1943

15

[1:20,000]

Canadian trials, over lines 160-497 km

1945

45

1:13,000

Italy, over 618 km, using 299,776 km/s for speed of light

5

1:120,000

Italy, results improved if value for speed of light changed to
299,793 km/s

1946

[17]

1:17,500

Aslakson tests with wartime system

[15]

1:20,000

Aslakson tests removing systematic error

1949

[4]

1:77,000

Best accuracy from Australian tests over 350 km and some 10
crossings

7

1:14,000

Accuracy of 7 parts per 100,000, concluded from Australian tests
of modified Shoran.

(*) Values in square []
brackets have been derived from the quoted value using a standard distance of
300 kilometres

Table 2 : Comparison
of Shoran, Hiran and Shiran
accuracies.

Hiran

Hiran
(officially HIgh-precision ShoRAN,
Rabchevsky 1984), but again sometimes unofficially HIgh frequency RAnging
and Navigation), was the technological evolution of Shoran but the
evolution also generated the more user-friendly Shoran sets of the late
1950s. These advances primarily reduced the workload of the airborne Shoran
operator. Aslakson (1951) stated that in February and
March 1950, the United States Air Force completed an extensive project in
Florida, wherein modified Shoran equipment was tested. Aslakson
(1980) further stated that following the last tests of the Hiran
equipment and the issuance of the final report of the 7th Geodetic Control
Squadron at Orlando, Florida, they considered themselves competent to undertake
an important geodetic connection across the Atlantic to Canada via the Greenland
Ice Cap. Much to Aslakson’s disgust, this project of
1950 was a complete failure due to inexperience resulting in insufficient
azimuth control being acquired. The resurvey was completed in 1956.

It will become clear that Hiran was only
used by the United States Air Force. Thus any other project said to have used Hiran had in reality used advanced Shoran, that is
the more user-friendly Shoran but without the addition of the resource overhead
of the complex ground and air gain-control instrumentation. Likewise, in the
early 1950s some surveys are shown as using Shoran when it is highly likely
that they were using Hiran before that name was
adopted, or even a mix of Shoran with later Hiran to
improve the final accuracy. Table 2 above was thus compiled on the basis of Hiran being used from 1950 by the United States Air Force,
Air Photographic and Charting Service.

It was claimed that Hiran could produce
surveys comparable in accuracy to first order ground triangulation. To
deliver its accuracy, however, Hiran needed more and
additional complicated equipment as well as a much larger number of highly
trained personnel than were required with Shoran. The modifications and
improvements made to Shoran to make it Hiran are
described in Aslakson’s 1951 paper New
Determinations of the Velocity of Radio Waves. As mentioned above, the
varying intensity or strength of the signal was the greatest source of error
with the Shoran system. Being able to monitor and maintain the signal strength
during measuring operations was an important feature of Hiran
and contributed to its increased accuracy of line measurement over Shoran.
However, it did come at a cost in both equipment and personnel. An auxiliary
oscilloscope was added to all ground and airborne sets along with an extra
operator. The operators continuously monitored and maintained signal intensity
for optimum measuring during line crossing. The pulsed Hiran
signal was also more focused, its amplitude more precise, and its phase
measurement more accurate. With a better means of calibration, Hiran was capable of achieving an accuracy of 1:100,000 or better than 8 metres on a line of 750
kilometres in length. Standardised procedures and computations saw that the
final Hiran network accuracy increased to around
1:150,000 or better.

This survey accuracy demanded massive resources and is why Hiran was only used by the United States Air Force. Hiran operations started with several Boeing RB-50 aircraft
(B-29 Superfortresswith major
modifications) as the airborne platforms. Each aircraft had a multidisciplinary
crew. The RB-50s regularly flew at altitudes of over 30,000 feet and on
occasions struggled to 43,000 feet to measure the longest of lines. Teams of
two to four specialists operated the equipment at the ground stations. There
was also significant logistical support that stretched right back to America. Hiran was essentially the most accurate airborne EDM of its
day but its use was highly specialised and extremely resource intensive.

Hiran
operations called for two sets of six line crossings at two separate altitudes
with atmospherics recorded simultaneously at the air and ground stations. The
line crossings yielded a least squares solution to the minimum distance between
the ground responders. The whole trilateration network was later adjusted to
provide coordinates for the unknown points in the network to better than 3
metres. The use of Hiran to survey an area was
generally mandated by the fact that the region could not be surveyed by any
other means then available. Further, locations for the siting of ground
stations was often solely governed by the locations of scattered islands so the
final network design was mostly less than optimal. This meant that rather than
the network comprising braced quadrilaterals having opposite sides of about
equal length and approximately 90° internal angles, the network comprised
mostly irregular figures. Such irregular networks were considered as not being
mathematically strong leading to the coordinates of the unknown points
having a reduced accuracy.

The United States Air Force adopted a process of strength-of-figure
computation. This involved a network design that would yield the results
required with minimum effort, verify the accuracy of the observed
measurements to determine the adequacy of the work and quantify the final
result. The probable error in the final coordinates of the unknown points could
be estimated using approximate map data and the probable error of a single
observed distance for which the Hiran network
planners took as ±0.0025 statute miles (4 metres). Different network designs
would yield different errors in the final coordinates. Such analyses were seen
as essential :

(a)

To ensure that the network was adequate to provide the desired
results.

(b)

To provide a guide to modifying the network. For example, if the
uncertainty in the longitude of a specific point was shown to be excessive,
the addition of one or more approximately east-west lines terminating at that
point would reduce that uncertainty. All apparent weaknesses in the figure of
the planned net were revealed and could be overcome before adoption of the
final network design.

(c)

To allow the adoption of an economical network figure. Excessive
strength in the latitude or longitude of any point indicated types of lines
that could be eliminated. Although the computation did not identify an
optimum network, iteration with different network constructions indicated the
best possible design.

(d)

To determine the necessity for the inclusion of azimuth control
and where such control would provide extra strength. The effect of an azimuth
line would be indicated by including an azimuth condition equation in the strength-of-figure
computation.

The Hiran ground personnel included
computing elements to permit comprehensive analyses and checking to proceed as
results became available. With the lack of any independent checks on the
accuracy of observations, the internal consistency of the network itself had to
be the primary method of field analysis. This ensured that any errors were
rectified while the ground parties were still in place and ultimately the
knowledge that the project had achieved its aim.

To establish an independent geodetic datum or to maintain the
orientation of a long arc of a Hiran survey, LOLA (LOngLine Azimuth) observations were
made on selected lines. At each ground station, observers would simultaneously
record the azimuth to the aircraft which was fitted with a special, high-intensity
flashing beacon. The beacon was installed in place of the original lower aft
gun turret, just forward of the tail skid. Such an installation induced extra
drag, thus the beacon was only installed for LOLA missions; please refer to
Figure 10 below. As will be seen, the flight parameters for a LOLA mission were
completely different to those of a line crossing mission. Accordingly, LOLA and
measuring observations could not be combined in a single flight.

On a LOLA mission, the angle at which the aircraft crossed the
imaginary line between the two observers was kept very small, approximately
five degrees. To the observers, the lateral movement of the flashing beacon
light then appeared relatively slow. Tracking of the beacon light was easier
and precision azimuth measurements could be obtained. As the line was crossed,
azimuths to the light were observed, using a photorecording
Wild T3 theodolite at each ground station. The azimuth recordings at the two
sites had to be made simultaneously. This was achieved by both theodolite
recording cameras being actuated by the same pulses being sent by radio from
the crossing aircraft. Twelve crossings were required for each line and were
averaged to determine the most probable reciprocal azimuths for the imaginary line
connecting the two stations.

Prior astronomic observations for position and azimuth at both
ground stations, provided the reference azimuth for the observations to the
aircraft beacon as well as to allow the application of the Laplace correction.
Azimuth data obtained during the crossing were processed using the SODANO
technique to solve for the reciprocal azimuths from the two stations. The
technique was named after Emanuel Michael Sodano who developed a rigorous and
non-iterative inverse solution of very long geodesics for computation by desk
calculators. The computation required no special tables and was accurate to the
tenth decimal place of radians for the azimuths and distance. In practical
terms this equates to less than 0.01 seconds of arc and less than 1 metre in
distance. The technique was also later used in electronic computing. The term SODANO
azimuths or lines is also in the literature to describe such
determined azimuths. LOLA measurements successfully determined the azimuths of
lines as long as 350 kilometres to within one second of arc.

Figure 10 : Photographs
showing the high-intensity flashing beacon, installed in place of the lower aft
gun turret just forward of the tail skid, used in LOLA observations.

Figure 11 : Map
showing major Shoran, Hiran and Shiran networks along with world triangulation and traverse schemes, after Rankin (2016) modified from US Army Topographic Command July 1971. Note the networks in Western Australia, Queensland, and the Great Barrier Reef, Australia plus some in Canada were acquired using Aerodist.

Major Hiran networks (refer map at
Figure 11) included :

Caribbean Island Tie : Between 1951 and 1953, Hiran
was used on a network which tied Florida with the Bahama Islands, Cuba, Haiti,
Dominican Republic, and Puerto Rico south to Trinidad and South America. This
work provided a tie between North and South America independent of the
conventional overland tie through Central America. In addition, the network
allowed the Inter-American Geodetic Survey (IAGS) to extend the North American
Datum 1927 (NAD 27) into Cuba. This project determined that Grand Bahama
Island, lying 60 miles off the Florida coast, was then shown on charts six miles
out of position. Cuba was also misplotted by 0.6
miles. The positions of other islands were also erroneously represented on the
charts. After the network was adjusted on the North American Datum 1927 an
overall accuracy of 1:113,000 was quoted as being achieved. A map showing the
northern section of this work is at Annexure A, Map A2.

Eastern Mediterranean Tie : In 1952 the United States Army Map Service initiated
a project for a geodetic connection between North Africa and the Greek
triangulation in the Aegean Sea. The network specifically tied the islands of
Crete and Rhodes with Libya and Egypt. The Eastern Mediterranean Tie
strengthened the existing triangulation around the Eastern Mediterranean, then
being readjusted, by a direct tie with the adjusted European net across the
Mediterranean Sea. The connection was carried out in the summer of 1953 by the
United States Air Force in cooperation with the Greek Army Geographical Service
and the Survey of Egypt. A map showing this work is at Annexure
A, Map A3.

North Sea Tie : Also in
1952, and again at the request of the Army Map Service, and in cooperation with
the Ordnance Survey of Great Britain and the GeografiskeOppmaling of Norway, a direct connection between the
triangulation of the British Isles off Scotland and the Shetland Islands, and
that of Norway was made. The North Sea Tie closed the loop of existing
triangulation around the North Sea. A map showing this work is at Annexure
A, Map A4.

North Atlantic Tie
: Completed in 1956, this network connected the North American
Datum 1927 to the European Datum, from Canada to Scotland and Norway by way of
Greenland, Iceland and Baffin Island.

Mid-Pacific Survey
: In late 1958, a Hiran network was
completed con­necting Wake Island, Kwajalein and Eniwetok Atolls, and the Taongi Islands.

Cuba-Central America Tie : Also known as the Yucatan Tie, this survey
was completed by the close of 1959.

Japan-TaiwanTie :
Between October 1959 and February 1960, a Hiran
survey stretching from Japan south­ through the Ryukyus
island chain to Okinawa, and then westward to Taiwan, was completed. This
network established a geodetic tie between the datum at Tokyo (Japan) and the Koshizan datum of Taiwan.

Brazil-Venezuela Tie : During 1960, a precise geodetic tie across a
large gap in the existing ground triangulation of northeastern
South America was made. The region was a strip 1,700 miles long and 500 miles
wide across the countries of Venezuela, British Guiana, Surinam, French Guiana
and Brazil. Within this region lay almost inaccessible terrain because of the
mouths of the Amazon and Orinoco Rivers, rainforest, jungle, savannah, and
mountains.

Eastern Pacific Tie : The Hawaiian Archipelago, along with Midway
and Johnston Islands were connected by Hiran and
established on a common datum. This long narrow network had no connection with
any existing datum, so it was necessary to ascertain the astronomic azimuth of
16 of its lines. Azimuth of 11 of these lines were accomplished by LOLA, with
the azimuth of the remaining 5 lines determined by traditional methods. The
survey was completed by 30 June 1962.

Southwest Pacific Survey : This extensive Hiran
survey was undertaken between 1962 and 1964 and tied Australia with Papua New
Guinea, the Bismarck Archipelago, the Caroline and Marshall Islands, the
Gilberts (Kiribati) and the Ellice (Tuvalu) Islands, and Fiji. This survey,
also known as project AF60-13, included some of the longest Hiran
lines ever measured, with the longest and Hiran
record being 576 miles (930 kilometres). To achieve these long distances, the
Boeing RB-50 aircraft as shown in Figure 12, had to get special approval to
exceed their operating limit of 37,000 feet and struggle to 43,000 feet. A map
showing this work is at Annexure A, Map A5.

Figure 12 : Left is
a Boeing RB-50 used on the Southwest Pacific Survey at Jackson Field, Port
Moresby PNG in 1963; Right, is a Hiran ground station
operator surrounded by the necessary measuring and communications devices
(Courtesy of George JeffFlemming).

In addition to the countries listed above, Hiran
Aerial Survey Teams also operated in Spain, Ecuador, Colombia, Peru, and
Vietnam.

Shiran

A further development of Shoran/Hiran in
1965 was SHIRAN (S-band Hiran). Shiran formed part the Kollsman
Instrument Corporation’s photomapping and electronic surveying system as shown
in Figure 13. Designated AN/USQ-28, the system was considered the most sophisticated
ever built, and operated in the late 1960s and early 1970s. Four such systems
were installed in Boeing Stratolifter RC-135A
aircraft, becoming operational in 1967. The Boeing Stratolifter
RC-135A was developed from the KC-135A Stratotanker,
both of which were derived from the Boeing 707 prototype. The RC-135A could
cruise at 855 kilometres/hour at an altitude of 10,700 metres for 7,400
kilometres.

Unlike Hiran’s pulsed emissions, Shiran emitted a continuous wave from the airborne master unit
at an amplitude modulated frequency of 3.312 GHz (S-band). Up to four ground
responders were sequentially interrogated in turn 10 times/second. The
amplitude modulation at four frequencies between 664 kHz and 161 Hz allowed the
distances to each of the ground responders to be measured at four different
wavelengths. Thus aircraft to ground distances were accurate to about 1 metre.
The measurement data were recorded on magnetic tape and processed by an
electronic computer which could be installed on the airborne platform itself.
The system was capable of generating, in near real-time, the coordinates
of one of the ground stations provided the coordinates of the other three
ground stations were already known. Shiran did not
replace Hiran completely, but was used on a 1970
survey of the interior of Brazil.

The RC-135As with their AN/USQ-28 systems could also undertake
aerial photography, radar terrain profiling, and as required could be fitted in
the field with a Beacon Lamp pod for long line azimuth (LOLA)
observations. Such a capability theoretically meant that an airborne survey
could be completed for an area about the size of Tasmania in a couple of weeks.

During 1972, however, the four RC-135A photomap­ping aircraft were
converted to other uses as the cost of upkeep for photomapping could no longer
be justified. The United States Air Force finally deactivated its Hiran/Shiran surveying capability
in 1974 when satellite positioning became available.

Formation of the National Mapping Council (NMC) in 1945 was
followed by the Council’s first meeting in the September of that year. The
chair for the meeting was Frederick Marshall Johnston, then Director of
National Mapping as well as Commonwealth Surveyor General and the
Commonwealth’s Chief Property Officer. To assist Johnston with the National
Mapping role, Bruce Philip Lambert was appointed Deputy Director of National
Mapping in late 1946.

An early priority for the NMC was a national geodetic survey.
However, Australia’s overall size and the vast sparsely populated regions to be
surveyed meant that much of the mainland would be without geodetic survey
control for some time. Airborne EDM was considered as a potential means of
rapidly extending control from the proposed geodetic survey. An airborne EDM
system would allow connection to areas where more intensive surveys would be
required and at the same time permit a series of widely scattered survey points
to be fixed. This national framework would form the basis for controlling the
surveys for any areas of isolated development.

Almost immediately after his 1946 appointment as Deputy Director
of National Mapping, Bruce Lambert travelled to the United Kingdom, Canada and
the United States to see how their national mapping agencies operated. He also
wanted to gain an understanding of their use of radar for geodetic survey.
This interest in the use of radar based EDM for surveying, mapping and aerial
photography was not limited to the National Mapping Section of the Department
of Interior where Lambert was based. Then Director of Military Survey, Colonel
Lawrence Fitzgerald, explained to the congress of the Australian and New
Zealand Association for the Advancement of Science held in Adelaide in 1946,
that considerable interest was being taken in recent developments in the
application of radar to surveying. Such was the Survey Corps interest that two
of its officers, Major HA Johnson (who was later to join National Mapping) and
Lieutenant FD Buckland, were sent to England at the end of that year. Their
task was the specific study of radar aids to mapping. While overseas during
1947, the two Army officers also went to Kenya in July for two months to
observe, the previously described, radar-controlled air survey task being
performed by the British. The RAAF was also interested in becoming involved
with the new technology. Around this time, two of its officers were also sent
to England to gain maximum knowledge of the new radar systems.

At least one driver behind these study tours appears to
have been resolutions adopted by the Commonwealth Survey Committee (CSC).
Although formed in 1935 as the government’s response for a coordinating body to
control now disparate Australian survey and mapping activities, the CSC did not
really meet, due to the war, until August 1944. The CSC was chaired by the
Commonwealth Surveyor General, with representatives of the three Defence
services (Navy, Army and Air Force). Coordination with the States was achieved
through the Commonwealth Surveyor General. For some years, the CSC and the NMC
operated in parallel before the CSC was finally abolished. CSC resolutions,
numbers 15 and 33 were likely adopted at 1945 meetings of the CSC and read :

No.15 - That this
Committee, having heard the views of Dr E.G. Bowen on the application of radar
to surveying, inform the C.S.I.R.O. of the Committee's keen interest in the
subject and recommend for favourable consideration by the Council a proposal
that further research be made into the design and use of radar equipment suited
for survey purposes under Australian conditions [Dr Edward George (Taffy)
Bowen (1911-1991), was then Chief, Radiophysics
Division of CSIRO (Bhathal, 2014)].

No.33 - That this
Committee notes the development of the application of Radar to surveying,
particularly with reference to aerial photography, and considers that the
conditions existing in Australia and the Territories warrant the introduction
of this equipment at the earliest possible moment, and recommends that the
R.A.A.F. adopt the Radar Control method of photographic air surveys, and be
responsible for selection and procurement of the most suitable air and ground
equipment, and operation and maintenance of this equipment.

After returning from his four-month overseas study tour, Lambert
was upbeat about the use of radar for mapping. In Canberra on Thursday
17 October 1946, he gave an address based on observations made during his
overseas trip. Lambert’s address was titled: Modern Developments in
Surveying and Mapping. It was presented at the closing of the conference on
Mapping and Survey Problems. Conference attendees included Surveyors General
from all states and the Commonwealth Surveyor General. Lambert’s address was
reported on page 4 of the next day’s Canberra Times under the headline RADAR
TO SPEED COMPLETE MAP OF AUSTRALIA. In the report, Lambert is quoted as
saying war-time developments of radar and radio will prove invaluable to the
future when carrying out national survey and mapping schemes and should be of
great assistance in extending the small area which so far has been adequately
mapped in Australia.The complete article is at Figure 14 below.

Figure 14 : Article from
page 4 of The Canberra Times of Friday, 18 October 1946.

At its
third meeting on Monday 14 October 1946, the NMC resolved to appoint the
advisory committee on the Radar Triangulation of Australia. The committee under
the chairmanship of Dr Richard van der Riet Woolley,
Commonwealth Astronomer, comprised Dr Joseph Lade Pawsey
and Dr Jack Hobart Piddington of the Radiophysics Division of CSIRO, Colonel Lawrence
Fitzgerald, Director of Military Survey, and Mr Bruce Philip Lambert, Deputy
Director of National Mapping. Their brief was to advise on the practicability
of using radar to create a framework of accurately surveyed points over the
whole of mainland Aus­tralia. Such a framework would enable all survey and
mapping activities to be coordinated on a national basis. This committee met at
the Commonwealth Observatory, Mt Stromlo on Tuesday 17 December 1946, and
discussed the problems involved and arranged for the necessary investigations
to be undertaken.

Over a
year later on Monday 2 February 1948, Fred Johnston the then Commonwealth
Surveyor General and Director of National Mapping, addressed the Rotary Club of
Canberra. His address was reported on page 2 of the next day’s edition of The
Canberra Times under the headline RADAR MAPPING PLANNED FOR AUSTRALIA.
Johnston was quoted as saying new equipment is on order by the Commonwealth
Government and, when it arrives, mapping by radar will become an established
fact in Australia…the use of radar for mapping purposes was availed of during
the war years overseas and it provided unbounded possibilities. While it
was not entirely clear, most likely the equipment Johnston had talked of was
the Radio Corporation of America (RCA) Shoran aircraft set AN/APN-3 and two
ground responder sets AN/CPN-2. This equipment was used to evaluate Shoran for
obtaining Australian survey and mapping control. Please refer to Annexure
B for the details of the equipment.

Subsequent
to the NMC establishing the advisory committee on the Radar Triangulation of
Australia, a subcommittee of the NMC was tasked with assessing whether Shoran
would provide a means of accelerating the Australian mapping program. This
subcommittee arranged with CSIRO to carry out tests using Shoran. Radar expert,
John James Jack Warner of the Division of Radiophysics
carried out and reported on the Shoran testing. Warner adopted a methodology
briefly described by Edward George Bowen, then Chief of the Radiophysics
Division of CSIRO, in his 1947 paper Radar Aids to Surveying.

The criterion
for acceptance of Shoran for airborne trilateration was a line measurement
accuracy in the vicinity of 1:100,000 or 1 metre in 100 kilometres. As it was
already known that the best accuracy was only around 1:50,000, extracting a
fifty percent improvement from the system was a big ask. The line
crossing technique was used with multiple line crossings at varying altitudes.

A
suitable braced quadrilateral, wherein all six distances were already known
from previous, high accuracy, ground survey, was selected in New South Wales.
The quadrilateral had its vertices near Condobolin, Tamworth, Sydney and
Canberra, as shown in Figure 15 below. The lines to be measured ranged from 158
to 311 miles (250 to 500 kilometres).

The
testing was documented in Warner (1950) which recorded that the airborne
equipment was installed in a Douglas Dakota C47B aircraft, flown and maintained
by the Royal Australian Air Force’s, Aircraft Research and Development Unit
(ARDU).

Additional
instruments were added in the form of a radar altimeter and equipment capable of
measuring meteorological parameters in flight. A Pilot's Direction Indicator
was a late addition. It consisted of a pair of counters, one recording the sum
of the two air-ground distances, and the other the difference. By flying the
aircraft so that the difference counter remained constant the aircraft’s track
was suitable for line crossing. Since the sum of the two distances was a
minimum at the crossing point and increased on either side, the sum counter was
used to indicate to the pilot that he had flown far enough on either side of
the line to permit a satisfactory record of the line crossing to be obtained.
This device also enabled operations to be carried out when the ground below was
obscured by cloud.

The
ground station responders were initially installed in trailers with one
subsequently installed in the back of a covered truck. Figure 16 below, is
understood to show one of the ground station equipment trailers with its aerial
in the stowed position; the antenna could be raised for measuring operations.

Figure 16
: Photograph understood to show one of the Shoran ground station
responder trailers containing an RCA Shoran responder AN/CPN-2 unit on-site
with its aerial in the stowed position.

The line
measuring operations required 18 months to complete with a total of more than 150 line crossing measurements taken over the six lines.
Overall an accuracy of about 7 parts in 100,000 or some 20 metres over a 300
kilometre line was achieved. This accuracy equates to about 1:15,000 with even
the best result only 1:77,000. An individual
measurement on any one line was considered to be within about 7 metres.

This
Australian test gave accuracy results comparable with those obtained elsewhere
and reinforced the fact that Shoran’s systematic equipment errors proved the
main limiting factor in obtaining higher accuracy. Warner suggested that by
suitable modification to the equipment, in particular to the receivers, the
signal intensity error could be reduced [and] the overall accuracy of
the technique would improve to about 2 parts in 100,000. An improvement on this
latter figure would be impossible without extensive improvements to the radar
equipment, particularly to the phase shifting goniometers and the display. In
addition, a thorough investiga­tion of problems of atmospheric refraction would
be necessary. Some similar such improvements to Shoran had already been
undertaken by the Americans to develop their Hiran
system.

Rimington and
others (1954) stated whilst these [Shoran] tests were being carried
out, a representative of the National Mapping Office acted as an observer, to
try and gather some idea of the econ­omics of the whole problem. The facts that
he gathered in regard to the opera­tion of the equipment were such that the
subcommittee on Radar could not recommend the method as an economic
proposition. It was felt by the subcommittee that the demands on money and
manpower required to use Shoran for mapping purposes would be beyond the very
tiny resources of the existing National Map­ping Office.

Lines
(1992) wrote that the ultimate decision to abandon Shoran for geodetic work
came in 1949. The reasoning behind the decision was that :

-

the
required accuracy was not attainable;

-

extending
radar trilateration over long distances into unsurveyed inland Australia without
some intermediate or end geodetic based check or azimuth control, was an
unsound survey technique;

-

the
ground equipment was relatively bulky and heavy, and required heavy vehicle transport
limiting the locations on where it could best be located;

-

costs
were uncertain, and beyond the financial and personnel resources then
available to the National Mapping organisation.

While a
pragmatic decision given the facts, it no doubt came as a blow to
Lambert and others who until now had been proclaiming the benefits of radar
based airborne EDM.

Rimington (1960)
noted that at about this time Dr Erik OstenBergstrand had demonstrated his first models of the Geodimeter, and it was decided to acquire and test a
production model of the instrument before finally deciding on a type of
electronic distance measuring equipment for use in Australia. A unit of the
equipment was obtained in 1953 and thoroughly tested with results that have had
great significance. The results of these tests, which agreed consistently with
those carried out in other countries of the world, established that electronic
measurement of the lengths of normal geodetic lines was not only practicable
but also had a phenomenal degree of accuracy. It was considered a remarkable
advance over Shoran airborne electronic measuring equipment, which relies on
extreme length of line (up to 400 miles) to achieve its fractional accuracy. It
was established that the Geodimeter
Type NASM-1 could measure distances with a limiting error of ±0.08 feet
(approximately ±1 inch or ±24 millimetres). Here then was a system that could
eliminate the time consuming base line and its associated network, substituting
the direct measurement of a single side of triangulation for all such base
lines. Figure 17 below, shows an example of the complexity of a traditional
National Mapping base net near Broken Hill in 1954. The red line North
Base-South Base was to be measured to a high precision with a special steel
band. Then by observing the internal angles of the blue network of triangles
the length of the major triangulation line Moorkaie-Sundown
could then be derived to an equivalent accuracy. The timely introduction of the
Geodimeter meant that the green line Twenty Mile-Felspar could now be measured rather than this complex base
net thereby achieving the same outcome in days rather than weeks.

Figure 17 : Example of a traditional
National Mapping base net near Broken Hill in 1954.

The red line North Base-South Base was to be measured to a high precision
with a special steel band. Instead the green line Twenty Mile-Felspar was measured by Geodimeter
EDM.

Control
for Australian mapping now followed a more traditional route of geodetic
triangulation and flexible, priority based, position-fixing by astronomical
observation. History shows that other interested members of the committees
likely took note of the outcome of the Shoran testing. Even the Royal
Australian Survey Corps, who were also initially interested in airborne radar
EDM and whose resources were greater than National Mappings’, continued with
traditional survey and mapping methods.

Nevertheless,
in late 1952, the first Australian application of Shoran to control mapping was
for a project in the Rum Jungle area of the Northern Territory. Accurate planimetric maps were required to serve as a base for
prospectors' charts, at a scale of one mile to an inch, showing radioactive
anomalies obtained from airborne scintillometer surveys conducted by the Bureau
of Mineral Resources. The West Australian newspaper of Thursday 31 July
1952, announced on page 7, Uranium Field to Be Air-Plotted…The Rum Jungle
uranium field in the Northern Territory is to be plotted soon from the air by
geophysicists of the Bureau of Mineral Resources. A Dakota aircraft, fitted
with equipment recently delivered from Canada and America, will be used…the
expedition will have its headquarters at Darwin and the aircraft will fly
courses that permit continuous readings along lines half a mile apart. To
ensure accuracy, the pilot (Capt. lvoDuffell, of Trans-Australia Airlines), will navigate by an
electronic aid, developed during the war, called "shoran".

For the
Rum Jungle surveys, the airborne equipment, including the Shoran AN/APN-3, was
carried by the Bureau of Mineral Resources’ Dakota aircraft VH-BUR. Two Shoran
responder, vehicle-borne units (AN/CPN-2) provided fixed ground control. The
Shoran units were loaned by the Radiophysics
Laboratory of CSIRO, Sydney and were most probably the same units as used on
the 1949 evaluation described above. Before leaving for the Northern Territory
the equipment was tested around Melbourne. In the Northern Territory the
vehicle-borne responders were set up near Mt Peel and Mt Tolmer,
a distance of 28.26 miles (45.5 kilometres) apart and about twenty miles or
thirty kilometres north-west and south-west, respectively, of the then Rum
Jungle mining camp. This camp was about 10 kilometres north of the present day
town of Batchelor. Please refer to map, after Wood and McCarthy (1952), at Figure 18 below.

Figure 18 : Map of 1952 Rum Jungle survey
area showing locations of Mt Peel and Mt Tolmer Shoran
responders in relation to Adelaide River, the then nearest town. The airstrip
marked in blue is today used to service the town of Batchelor situated just to
its north. The then Rum Jungle mining camp was about 10 kilometres north of the
airstrip.

From BMR’s
perspective they were happy with the outcome of the survey and stated with
the Shoran equipment it is possible to pin-point radio-active areas
sufficiently accurately to enable ground parties to locate them. This reduces
the amount of ground surveying to a minimum and so speeds up greatly the rate
at which an area can be investigated. The Melbourne Age newspaper
reported on the spectacular results of the Bureau of Mineral Resources’
surveys. The Bureau, who had used Shoran positioning during their 1953 airborne
surveys, and had been successful in their search for oil in Gippsland, iron on
the Eyre Peninsula, and copper on the Yorke
Peninsula.

From
National Mapping’s perspective the Rum Jungle survey results were not so
exciting. The details are in a 1954 paper by Rimingtonetal: Application of Shoran to Australian
Mapping. A major failure of the project was that the F24 camera installed
in the aircraft to provide positioning photography was subject to
aircraft movement, tip and tilt, thus the air position coordinates provided by
Shoran could not be accurately transferred to the ground. The Shoran system had
not been able to meet the Australian geodetic specifications. However, in that
era the radar based technology was still of great interest. If pursued,
technical advances might soon make radar useful to surveying and mapping
Australia’s vast landmass. The extent of this interest was evidenced by the
terms of reference for the Brown report containing a specific requirement that
Brown’s investigation: should cover the following technical matters…the
implications of the adoption of radar triangulation on the national system.

Major-General
Reginald Llewelyn Brown, then Director General Ordnance Survey of Great Britain,
finished his report to the Minister for the Department of the Army in December
1951. At the invitation of Australian authorities, Brown had visited Australia
in early 1951. He had met with State and Federal mapping agencies to gain the
information vital for him to formulate the advice required under his terms of
reference.

Regarding
radar, Brown covered the uses of radar for surveying in war; the value of radar
in the geodetic framework, he cited Canada’s Shoran experience and supported
Lambert’s 1946 view detailed above. Brown also covered air photography and
radar techniques. Brown concluded: it does not seem likely that radar
triangulation will ever be able to replace geodetic triangulation
altogether…the present radar technique is unable to measure short distance.
Furthermore, radarcannot be related with sufficient accuracy to
astronomical observations for azimuth. It should not therefore be allowed to
delay any projects for geodetic triangulation. In his recommendations to
the Minister, Brown stated experience in radar triangulations be gained
within Australian territory as soon as possible and that geodetic triangulation
be not delayed on that account. Hindsight shows that, as discussed further
on in this paper, radar technology was the way forward as within 5 years highly
portable terrestrial EDM was available followed by airborne EDM about 5 years
after that.

Following
his four year term as Director General of Ordnance
Survey, Brown retired in 1953. In retirement, Brown consulted to Spartan Air
Services of Canada for their work in Europe and the Middle East which included
aerial photography, magnetometer, scintillometer, electromagnetic, Shoran and
Airborne Profile Recorder surveys. When, in 1963, Spartan bought an interest in
Meridian Airmaps Limited, Brown was appointed
Chairman. In 1973, Meridian repurchased the Spartan interests and Brown
continued as Chairman of the company until his death in 1983.

Based on
the results of the Bureau of Mineral Resources’ 1952 use of Shoran, the technology
was adopted for positioning in resource exploration. The Bureau of Mineral
Resources used advanced Shoran (AN/APN-84 and AN/CPN-2A). These were
later models than those used for the 1949 and 1952 work. The advanced Shoran
models became available in the mid-1950s. The AN/APN-84 master station was
fitted in the aircraft and three AN/CPN-2A responder stations were fitted into
Morris Commercial, four wheel drive trucks. The
aircraft master interrogated two ground responders at a time to give a continuous
fix of the aircraft's position. The ground responder sets were
positioned as close as possible to previously fixed survey stations.
While two of the ground responders were in operation the third could be
repositioned, permitting almost continuous flying operations.

The
Bureau used this system for positioning in the offshore Perth Basin in 1957,
Carnarvon Basin in 1956 and 1957, Broken Hill district during 1957 and 1959,
the Bonaparte Gulf Basin in 1958 and Tennant Creek Mineral Field in 1960. Later
in 1961, Haematite Explorations Pty Ltd used Shoran as a navigational aid for
the offshore survey of the Bass Strait as did the Texaco Overseas Petroleum
Company in 1969 in the Papuan Basin in the Torres Strait. In 1968, the Western
Geophysical Company of America was the prime contractor and operator for Esso
Standard Oil (Australia) Limited (the phonetic version of the initials of
Standard Oil i.e. SO or Esso and the American trade name for
ExxonMobil). Offshore Navigation Incorporated was subcontracted to provide
survey control using Shoran for the marine survey of the Otway Basin of
south-west Victoria. Offshore Navigation Incorporated also operated off shore
in the north-west of Western Australia around 1965. By the late 1960s, however,
more sophisticated and accurate methods of navigation/position fixing
had been introduced.

NatmapAerodist line measuring operations for Block 36 took place
in 1973. This work extended survey control offshore around Onslow. On Tuesday
28 August 1973 an existing station Shoran 11 was occupied and
intersected by lines from mainland stations Onslow (R299) and Minnie
(KAP8). Station Shoran 11 was also spot photographed from 3000 feet.
None of the readily available information mentions station Shoran 11 but
it was probably established for exploration activities. National
Archives Australia hold a series of records in Perth from 1966, titled Survey
and mapping - Shoran Survey - Onslow - Barrow Island - Station notes. The
Recording Agency is listed as 5 Field Survey Squadron, Australian Army, and the
Controlling Agency, Defence Corporate Services and Infrastructure Centre,
Western Australia. Station Shoran 11 could thus have been established by
the Squadron.

National
Archives Australia also holds records indicating that National Mapping fixed
points for later occupation by the Bureau of Mineral Resources Shoran ground
responders. The points were in the Rum Jungle, Tennant Creek and Broken Hill
areas. In his 1979 paper, The Division of National Mapping’s Part in the
Geodetic Survey of Australia, Ford makes mention of the Eyre Peninsula, Rum
Jungle and Broken Hill surveys also being required by the Bureau.

It would also appear from the way events unfolded, that the 1945 Commonwealth Survey Committee resolution 33 recommending that the R.A.A.F. adopt the Radar Control method of photographic air surveys, went ultimately unsupported by the National Mapping Council. An article in the Melbourne Herald newspaper of 11 September 1945 had predicted that within a year…radar…will be used to control the shutter of the aerial camera so that the exact position of the plane and details of the landscape photographed will be known…to within 17 yards' accuracy. As already mentioned above, both the Army and RAAF sent officers to the UK to evaluate their acquisition of radar controlled mapping. The fact that Shoran was evaluated for use in Australian mapping by the National Mapping Council, leads to a conclusion that the older UK Gee-H technology was indeed by now inferior to the more advanced Shoran. In the final analysis however, even Shoran failed to deliver the required accuracy for Australian mapping control.

By the
mid-1980s, the use of terrestrial or airborne radar EDM systems in Australia
for surveying and mapping had already passed into history by some ten years. It
was therefore surprising to find Bowen’s 1987 description of events as is
reproduced at Annexure C below. Suffice it to say that
Bowen’s account reflects that described in his 1947 paper rather than what
actually happened, as was detailed above!

Horizontal
Mapping Control from Fully Oriented Aerial Photographs

A persistent vision in National Mapping was to provide horizontal
mapping control without having to have a survey party occupy the actual control
points. The theory ran that by taking aerial photographs of the region where
the mapping control was required, accurate coordinates of feature(s) in the photoframes could be calculated. However, the coordinates
of the positioning camera platform at time of exposure was required as was the
camera’s orientation, tip and tilt, as no aerial photograph was truly vertical.
As was found in the 1953 Shoran based work in the Northern Territory, described
above, the major obstacle lay in determining the positioning camera’s
orientation at the time of exposure.

McLean’s (2015), The Aerodist Years
described the next attempt using Aerodistphototrilateration. Even with the addition of a special
horizon camera, the tips and tilts of the then Vinten
positioning camera could not be determined accurately enough to provide
suitable ground control coordinates.

Around 1975 came an internal NatmapProposal
for Linear Edge Control of Photogrammetric Blocks, please refer to Annexure D below. The proposed method to obtain mapping control
by photographic means was never implemented. The proposal document also
mentioned another project that was to provide the tip and tilt of an aerial
survey camera at time of exposure, namely the Camera Attitude Indicator
(CAI).

The National Mapping idea of the CAI was given to the Department
of Supply’s Weapons Research Establishment (WRE) for operational development.
WRE had already developed and was maintaining WREMAPS1 (the Laser Terrain
Profiler) for Natmap. Thus, both organisations had an
ongoing relationship at the time. WRE gave the project the name TAVRS for Twin
Axis Vertical Reference System. The different names
could get a little confusing at times, depending on to whom you were speaking;
the CAI meant nothing to WRE and likewise the name TAVRS was largely unknown to
Natmappers. As part of the development, Natmap provided one of its Wild RC9 aerial survey cameras
and funded WRE’s development costs. This funding included the cost of WRE’s
sourcing of a surplus Ferranti inertial navigation platform that was produced
for jet-fighter aircraft navigation. Please refer to Figure 19 above. The
inertial platform was a sizeable piece of equipment in itself, having about the
same footprint as the RC9 camera but was twice the height. When the Ferranti
system was coupled with the RC9 camera it was a substantial and impressive
looking device.

To accurately measure the tip and tilt of the RC9 camera lens at
the time of each film exposure, the Ferranti system had to be fixed directly over
and connected to the RC9 camera body. One problem was that to load film into
the RC9 magazine, the magazine (which sat over the camera’s lens system and
focal plane) had to be raised. The Ferranti system prevented that function. WRE
overcame that problem by adapting the film magazine to side-loading. The
digital readouts from the Ferranti system were reflected into the
instrumentation panel of the RC9 camera so each exposed frame would contain the
required positional and angular data. However, the Ferranti system failed
repeatedly during bench testing. With the emerging GPS technology already on
the horizon, the CAI/TAVRS project was scrapped.

The idea that a GPS antenna might be attached to the nose and tail
and each wing-tip of the photographic aircraft and thereby use that technology
to measure the attitude of the aircraft at the time of photographic exposure
was considered, but never eventuated either.

The South African Finale - the Aerodist System

From the mid-1950s and into the 1960s and later, EDM equipment for
surveying and mapping emerged from South Africa. Just as a hundred years
previously when the steel band had replaced the Gunter link chain for
distance measuring, these instruments would have an even greater impact. No
longer would waterways, swamp, forest, jungle, be a barrier to the survey or
mapping team. Provided the two end points of a line were accessible and visible
to each other, measurement between the two points was possible; what was in
between was now largely immaterial.

The South African’s, to coin a phrase, killed two birds with
one stone. Colonel Harry Baumann, then Director of the South African
Trigonometrical Survey, wanted an EDM that was man-portable with a range
out to 50 kilometres and an accuracy of not less than 1:100,000. Bergstrand's Geodimeter was just too limited and too cumbersome having to be operated at night and from
locations that were vehicle accessible because of the weight. The 1957 Tellurometer by Trevor Lloyd Wadley of the Telecommunications Research Laboratory was the solution.

The rapid emergence of the Tellurometer was the likely result of
both Baumann and Wadley’s previous experience with radar systems. McLean (2015)
recorded that Baumann was familiar with radar and with the existing Shoran and Hiran long range EDMs. McLean continued and also recorded that during
World War II Wadley was initially part of the highly
secret Special Signals Service in Johannesburg that worked on the development
of radar systems. After specialised radar training in the United
Kingdom, Wadley was posted to an operating radar station in the Middle East as
the officer-in-charge. Here he worked successfully on improving the performance
of the station’s equipment. Some of Wadley’s war time activities were of a
secret nature and included working on the staff of British General Harold
Alexander during his command of the Fifteenth Army Group for the invasion of
southern Europe. It is highly probable that in addition to primary radar
development, Wadley’s secret work involved secondary radar like Gee and
possibly extended to the later Gee-H and even Shoran. Consequently, Wadley would
have understood the intricate shortcomings of existing radar for use in
surveying applications. His solution was to superimpose a low frequency wave on
the signal using a precise method of phase comparison and creating the basis of
the Tellurometer. Sales to Canada, Australia, the United States and numerous other countries resulted. The United States Army ordered several hundred Tellurometer instruments.

With intervisible lines now able to be measured almost without restriction, the focus turned to non-intervisible lines for which an airborne system would be required. The portability and range of the Tellurometer was the basis for the Aerodist (Aeroplane Distance)
system. At the beginning of the 1960s, Canada and particularly Australia saw Aerodist as a viable system for use in their mapping programs and used the system with great success.

Between 1963 and 1974, the Division of National Mapping deployed an Aerodist MRC2 secondary radar system to provide horizontal control for the 1:100,000 scale National Topographic Map Series. Nat Map used that system to obtain control over more than 50 per cent of mainland Australia and over some offshore areas. During the above period Nat Map's Aerodist system measured some 3,020 lines to fix the positions of 485 survey control stations. Nat Map's use of Aerodist is detailed in McLean's 2015 work The Aerodist Years. McLean (2015) also noted that the Royal Australian Survey Corps took delivery of an Aerodist MRC2 system in 1964. That Aerodist system was initially deployed in western Papua New Guinea. Subsequently RA Survey carried out Aerodist survey operations in Indonesia and in northern Australia including Cape York, Arnhem Land and the Kimberley. After the loss of its initial system in an aeroplane crash in November 1969, RA Survey updated its Aerodist system to the operationally more reliable computer assisted MRB3/201 equipment. The last field deployment of the Corps' Aerodist system was in 1975.

Concluding remarks

Essentially the Tellurometer and Aerodist
was EDM at its peak. Other models and even other instruments came along
afterwards using laser light rather than microwaves, solid state circuitry,
digital readout and even automated data recording and processing. These were
just improved versions of the basic concept.

In under twenty years, Aerodist
technology had thus miniaturised every aspect of then airborne EDM for
the measurement of non-intervisible lines of less
than 350 kilometres. Unlike the earlier airborne EDM technologies, Aerodist was an economic option for National Mapping to
employ for its 1:100,000 scale topographic mapping
control program. Ten years later as National Mapping was concluding its Aerodist surveys, positioning with the aid of artificial,
earth-orbiting satellites was already viable as a technology for providing
mapping control. Thus, all airborne EDM became obsolete.

Acknowledgement

Thanks to Laurie McLean for his research contributions and valuable comments on the draft
version.

Ford, Reginald Arthur (1979), The Division of National Mapping’s
Part in the Geodetic Survey of Australia, The Australian Surveyor, June,
September and December 1979: Vol.29, No.6, pp.375-427; Vol.29, No.7,
pp.465-536; Volume29, No.8, pp.581-638, ISSN 00050326, published by the
Institution of Surveyors, Australia. This work is accessible via this link

United States Coast and Geodetic Survey (1964), Geodetic
Operations in the United States and in other areas through International
Cooperation, January 1, 1939, to December 31, 1953, Report to the
International Association of Geodesy of the International Union of Geodesy and
Geophysics, International Council of Scientific Unions, Special Publication
No.320, Government Printing Office, Washington.

United States Army Air Forces (1945), Graphic Survey of Radio
and Radar Equipment used by the Army Air Forces, Air Technical Service
Command, AAF-MD-E89.

United States Air Force (1972), Various documents relating to USAF
Hiran surveys amounting to 2055 pages, Air Force
Historical Research Agency (AFHRA - http://www.afhra.af.mil),
contents of microfilm roll NO899, filmed on 27 July 1972, supplied on CD in
2014.

The first two pages describe the AN/APN-3, the airborne component
of the Shoran system. The final two pages describe the AN/CPN-2, a Shoran
ground responder unit. At least two responder units were required for line
crossing operations.

This annexure was extracted from United States Army Air Forces:
Graphic Survey of Radio and Radar Equipment used by the Army Air Forces 1945,
Air Technical Service Command, AAF-MD-E89.

Annexure
C

Radar
Aids to Surveying

Edward
George Bowen, circa 1987

The ability of radar to
measure distance to a high degree of accuracy was exploited during the war in
devices like the OBOE blind bombing system. This was a method by which a Pathfinder
aircraft over the Ruhr was positioned accurately by measuring its distance
precisely from two ground stations in Britain. An interesting fact soon
emerged. Conventional ground survey methods had reached a high degree of
sophistication well before the war and these had been used to link the British
survey to that of France, and that of France to that of Germany. It turned out
that the accuracy with which this had been done was much poorer than could be
measured by the OBOE system. The maps had, therefore, to be corrected, after
which an aircraft could then be placed with an accuracy of 20 or 30 yards over
particular factories in the Ruhr.

The
existence of such mapping errors was not forgotten in the immediate post-war
period. Australia, for example, is a continent with an area of which over half
is inaccessible and difficult to traverse, let alone survey with any precision.
It was known that even along the relatively well travelled Adelaide to Darwin
route there were occasional errors, not of yards, but of many miles in surveys
starting from the north as compared with those coming from the south. Up to that
time, the traditional methods of survey were almost entirely based on
triangulation, that is, building up a series of triangles from a single measured
baseline. The angles of each triangle were measured to a high degree of
precision but only occasional checks of distance were possible when the terrain
allowed it. In remote or inhospitable country, such checks simply could not be
carried out and the accuracy suffered accordingly. Radar provided an entirely
new dimension in that the triangulation could be established by the accurate
measurement of distance alone, made in sections of 200 miles at a time. It was
not even necessary to traverse the intervening ground; an aircraft could fly
over the terrain, position itself from two radar beacons on the ground and
simultaneously record its position by vertical photography.

These
methods were of inestimable value in remote parts of countries like Australia
and Africa which might contain minerals and other material needed by a
resource-hungry world. It is probably true to say that radar survey methods
were not much used in more developed countries which already had reasonably
accurate surveys, but they were enormously important in less developed parts of
the world.

This annexure was extracted from Edward George Bowen’s
1987 book: Radar Days

(Bowen was Chief of the Division of Radiophysics
in CSIRO, from 1949; around the time Warner and others
were investigating radar-based Shoran for surveying and mapping in Australia).

Annexure
D

PROPOSAL FOR LINEAR EDGE CONTROL

OF PHOTOGRAMMETRIC BLOCKS

Generally, most systems used to obtain horizontal field control
for photogrammetric mapping are directed to the acquisition of both X and Y co­ordinates,
usually around the perimeter of a block. Whilst this is mandatory in completely
uncontrolled areas, there are situations where the acquisition of either X or Y
values could assist. Australia, for example is covered, or shortly will be, by
a control grid on a one degree spacing, and there are
indications that this spacing is too great to provide the whole perimeter
control of block adjustment areas.

The grid, in itself, provides the essential control at the
corners of mapping blocks, particularly if they are in suitable modules of 1:250,000 scale map areas. Having the corner control so
readily available, it is only necessary to devise a scheme to restrain the bowing
or bulging which would normally occur along the edges in between this basic one degree control. It is proposed to do this by
figuratively stretching a string between these stations, i.e. by
providing a series of control photographs along a straight line between the
corner control points.

The spacing of the photographs along the piece of string
is not critical, only the fact that they are on the straight line is important.
In other words, it is proposed to control the perimeter bowing in
photogrammetric block adjust­ments by using a series of points whose northings
are accurately known, when spaced along a parallel, and whose eastings are
known when spaced along a meridian. The requirement to provide one accurate
ordinate only, instead of two, simplifies the field acquisition of control data
very substantially.

To achieve this, it is proposed to position a laser beam
drawn out into a vertical fan or wall, at an Aerodist
station, and to direct it towards a second station, along an approximate
azimuth derived from already established observations. The beam will miss the
second station by an unknown amount, which could be up to 30 metres if the
misalignment is about one minute of arc.

An aircraft carrying a vertical photogrammetric camera,
camera attitude indicator (in development) and a laser sensor is then flown to
approach the distant Aerodist station at right angles
to the laser wall, as shown in the diagram below. To determine the azimuth
correction of the laser curtain, the aircraft heading need only be approximate
as the offset of the nadir point from the Aerodist
station will be small and errors in heading not critical. On reaching the edge
of the beam, the camera will be triggered by the laser light or pulse being
detected by a sensor on the aircraft. The resultant photograph will record the
relevant positions of the nadir point, the Aerodist
station and the laser beam. A second picture can be exposed after a selected
interval to provide stereo coverage.

These initial pictures will enable a photogrammetric
evaluation of the misalignment of the laser beam to be made and to correct the
subsequent series of photographs if necessary. Any number of subsequent control
photographs can be provided by approaching the laser wall at right angles at
selected intervals, the laser beam firing the camera as before. All of these
points will lie on a straight line, and can be individually corrected to the
line joining the two Aerodist stations.

Looking at the proposal in more detail, the following
observations can be made :

It does not
appear that an excessively strong laser will be necessary. The Model 8 AGA Geodimeter, a small portable instrument, is capable of sensing
a laser beam over a double path of 60 km or a total distance of 120 km. In this
application a 5 milliwatt laser is diverged to 1.7 milliradians to enable the beam to be kept aligned with the
retroprisms in spite of atmospheric effects. It is
hoped that no divergence will be necessary in the proposed system, with the
possibility of using an even smaller laser power source.

The sensing
device in the same AGA Geodimeter is not very large
and even if the airborne sensor has to be enlarged, it should still be possible
to keep it relatively small. The size of this sensor is discussed in detail
further on.

Aerodist
stations are cleared to have an unobstructed view above 1.5 degrees
elevation. As the proposed flying height of the camera aircraft is a maximum of
3,000 metres and the maximum range is about 100 km, this should not present any
difficulty.

The laser
beam can be drawn out into a fan by two means either optically; by using a
cylindrical astigmatising lens or mechanically; by a
number of tangential mirrors on the periphery of a rotating wheel. To ensure
that a laser pulse reaches the aircraft camera sensor to trigger the camera at
the right instant, the size of the sensor must be based on the number of
mirrors, their rotational speed, and the speed of the aircraft. Thirty-six
mirrors mounted on a wheel rotating at 16,000 rpm would mean the transmission
of 9,600 pulses every second. However, the aircraft sensor would also be moving
at about 50 metres/second and would advance some 5 millimetres between pulses.
Thus to register a pulse, the aircraft sensor would have to be larger than 5
millimetres to ensure that sufficient pulses would trigger the camera.

The
verticality of the laser wall should not present a problem as a dislevelment of even 20 seconds of arc, representing 0.3
metres at the proposed flying height, could be tolerated. Gravity effects would
be smaller still.

The system
may be affected to some extent by prevailing conditions of visibility. However,
because the photographs produced are to be used for control purposes only, they
do not need to be of mapping quality. Advantage can therefore be taken of the
more stable visibility conditions prevailing early and late in the day even
though shadow lengths may be longer than desirable. Some detailed scheduling of
flying times will be necessary to maintain uninterrupted production, and to
take advantage of the most favourable flying conditions.

It is envisaged that large areas of Australia where the
road systems are adequate, could be covered by transporting the laser by
vehicle, with the camera and sensor in a light twin engined
aircraft. In less developed areas, the laser generator would probably be best
transported in a small helicopter. Each set up would provide 400 km of linear
control photographs in the four cardinal directions, with the result that only
alternative setups would be required through the basic control grid. In
addition to providing the peripheral control, supplementary lines would reach
into the area at right angles to the surround, adding even further horizontal
control to the photogrammetric block.

A photogrammetric block of 12 x 1:250,000 scale map sheet
areas could be controlled by occupying just 9 stations, as shown in the diagram
below, and provide 3,600 kilometres of control in a short space of time.

This annexure is a copy of an internal working paper developed by
the Control Survey Branch, Division of National Mapping, Melbourne circa 1975.